Add regression test for generic inference

[lsunsi]

Fixes #120922.

This PR tests the crash mentioned in the issue. The reduction was made with treereduce and it was quite drastic.
This code causes the same ICE as #120922 on 1.76, 1.77 and 1.78.
1.79 appears to fix it, and it doesn't cause ICE on stable either.

I couldn't figure out a good name for the test file so I just used the issue since there were others already doing that. But I could change it if there's a better name for it.

EDIT: I saw that tidy didn't like the test name, so I changed it to please it. But like I said, I couldn't think of a good name, so I'm open to suggestions.

[rustbot]

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